Inertia switch with manually adjustable conductive spring arm assembly

ABSTRACT

An inertia switch capable of detecting the arrival of stress waves from any direction in the plane of the mounting surface is disclosed. In a preferred embodiment, a plurality of conductive spheres are held in a plurality of corresponding recesses by spring arms. A pair of interconnected conductors on each recess surface form, with the conductive spheres, an electrical circuit which is broken if any of the spheres is moved outwardly of its recess against the spring by any impact or stress wave in the structure. Provisions are included for adjusting the switch sensitivity by adjusting the spring preload on the spheres.

United States Patent 1 1 1111 3,73m20 York 1451 May 1, 1973 [54] INERTIASWITCH WITH MANUALLY 2,921,999 1/1960 Ziegler, Jr. ..200/61.52

ADJUSTABLE CONDUCTIVE SPRING ARM ASSEMBLY Primary Examiner-J. R. Scott[75] Inventor: Kenneth C. York, Pomona, Calif. Attorney-Edward Johnson[73] Assignee: General Dynamics Corporation, [57] ABSTRACT Pomona Cahf'An inertia switch capable of detecting the arrival of [22] Filed: Jan.17, 1972 stress waves from any direction in the plane of the mountingsurface is disclosed. in a preferred embodi- [21] Appl' 218329 ment, aplurality of conductive spheres are held in a plurality of correspondingrecesses by spring arms. A [52] US. Cl.....200/6l.45 R, ZOO/61.52, 200/166 BE pair of interconnected conductors on each recess sur- [51] Int.Cl. ..l-l01h 35/02 face form, with the conductive spheres, an electrical[58] Field of Search ..200/61.45 R, 61.53, circuit which is broken ifany of the spheres is moved ZOO/61.11, 166 BE, 835, 835 A outwardly ofits recess against the spring by any impact or stress wave in thestructure. Provisions are in- [56] References Cited eluded for adjustingthe switch sensitivity by' adjusting th 1 (1 th h UNITED STATES PATENTSSpmg pre 6 Sp ms 2,741,674 4/1956 Richard ..200/61.45 R 15 Claims 8Drawmg Fgures 2,912,534 11/1959 Rowell et a1. ..200/61.45 R X 0, 54 l Ib 1 1 12 14 a 36 1 34 2 I2 33 32 I I 4 4.

66 4O 68 6O 64 I6 '62 38 7O Patented May 1-, mix- 4 Sheets-Sheet 1Patented May 1, 1973 4 Sheets-Sheet 2 FIG. 2

se 40 as so 54 I6 PIC-3.3

I Patented May 1, 19 73 4 Sheets-Sheet 5 98 I4 90 I6 FIG. 4

FIG.5

INERTIA SWITCII WITH MANUALLY ADJUSTABLE CONDUCTIVE SPRING ARM ASSEMBLYBACKGROUND OF THE INVENTION Inertia switches are useful in a number ofapplications. Such a switch will respond instantly to a suddenacceleration or deceleration of a predetermined magnitude. A typicalapplication is as a contact fuze for mortar or artillery shells. Inertiaswitches may also be used as safety devices, for example, to deenergizethe electrical system of an automobile or aircraft in the event of acollision, or to shut down pumps, etc., in the event of an earthquake ornearby explosion. Inertia switches may also be used to activate animpact recorder in shipping containers for delicate instruments to showthat permitted impact levels have been exceeded.

Many different types of inertia or impact switches have been developedfor these various purposes. However, these designs still have severaldeficiencies. Simple switches tend to be responsive to inertial forcesapplied from only a single direction. Omnidirectional switches tend tobe complex and unreliable.

The sensitivity of most prior inertia switches is low and generally nosensitivity adjustment is provided.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide an inertia switch of improved simplicity and reliability.

Another object of this invention is to provide an inertia switch capableof detectingstress waves from any direction in the plane of itssupporting surface.

Still another object of this invention is to provide an inertia switchhaving adjustable sensitivity.

The above objects, and others, are accomplished in accordance with thisinvention by an inertia switch in which a plurality of recesses areformed in a support member, each of which has two spaced conductors onthe recess wall, and conductive members, such as spheres, are positionedin the recesses in contact with the conductors. The conductors in theseveral recesses are interconnected so that with the members in place asingle complete electrical circuit is formed through all of theconductors and members. This electrical circuit is broken by movement ofany member outwardly of its recess. Thus, this assembly operates as anormallyclosed switch. A spring member mounted on the support has aplurality of spring arms which engage the members and bias them into therecesses. When the switch is subjected to acceleration or decelerationforces, inertial forces on some members will force them outwardly fromthe recesses against the spring force to open the circuit. Means areprovided to adjust the spring force holding the members in place, toadjust the sensitivity to stress waves. Preferably, the recesses areformed around the support axis facing outwardly in a single planeparallel to the mounting plane of the switch, so that the switch willreact to any stress waves traveling in that plane from any direction.While two spaced recess-and-member assemblies are often sufficient, forbest multi-directional sensitivity four evenly spaced assemblies arepreferred.

, The spring force adjusting means may be arranged so that all springarms are adjusted simultaneously, or individual adjustment of each armmay be provided. If

operated at temperatures as high as l800 F. The simplicity of thisswitch permits substantial miniaturization; if desired, the maximumdimension may be as little as 0.4 inch.

BRIEF DESCRIPTION OF THE DRAWING Details of the invention, and of apreferred embodiment, will be further understood upon reference to adrawing, wherein:

FIG. 1 is a prospective exploded view of the switch;

FIG. 2 is a horizontal sectional view of the switch taken on line 2-2 inFIG. 3;

FIG. 3 is a vertical sectional view of the switch taken on line 3-3 inFIG. 2;

FIG. 4 is a horizontal sectional view of an alternative embodiment ofthe switch taken on line 4-4 in FIG. 5;

FIG. 5 is a vertical sectional view through the switch embodiment ofFIG. 4, taken on line 5-5 in FIG. 4;

FIG. 6 is schematic horizontal section through the switch of FIG. 4taken on line 66 in FIG. 5, together with schematic side views of therecess conductor arrangement; and

FIGS. 7 and 8 are vertical sectional views through a portion of a switchillustrating alternative spring adjustment means.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there isseen an exploded view illustrating the component parts of the switchaccording to this invention. The switch is contained within a housing 10which has a pair of ears 12 extending outwardly at the opposite sides ofthe housing base.

Housing 10 includes a cavity 14 which is cylindrical near the top andbecomes inwardly-narrowing frustoconical in shape near the base, as seenin FIG. 3.

An insulating body generally designated 16, which may be formed from aceramic or other dielectric material, is shaped to conform to cavity 14.Upper cylincrical portion 18 fits loosely within the cylindrical portionof cavity 14, while tapered lower portion 20 of body 16 matches thelower frusto-conical portion of cavity 16 (as seen in FIG. 3). Thus, asbody 15 is pressed downwardly into cavity 14, the body is wedged tightlyand securely in place through the full range of temperature change.

Body 14 also has a pair of generally rectangular cutouts 22 and 23 onopposite sides and a dished upper surface 24. Generally U-shaped springmember 26 fits within cutouts 22 and 23, with the center portion 28bridging dished surface 24. As spring 26 is pressed downwardly, centerportion 28 rests on ridges 30 bounding dished surface 24.

A pair of inwardly extending conical recesses 32 and 33 are provided atthe lower ends of cutouts 22 and 23 (not seen in FIG. 1, but shown inFIGS. 2 and 3). A pair of conductive spheres 34 and 36 are positionedwithin recesses 32 and 33, respectively. As described below, spheres 34and 36 normally bridge spaced conductors within recesses 32 and 33 tofunction as normallyclosed switches. A pair of insulating pads 38 and 40on spring 26 press against spheres 34 and 36 to bias them into theirrespective recesses while insulating them from spring 26.

The open upper end of cavity 14 is closed with cover 42 which ispreferably welded to housing 10. Belleville spring-washer 44 iscompressed between cover 42 and shoulder 46 of body 16 to hold body 16firmly in place within cavity 14.

An adjusting screw 48 is threaded through an opening in cover 42 to bearagainst center portion 28 of spring 26. As best seen in FIG. 3, as screw48 is moved downwardly, center portion 28 of spring 26 is moveddownwardly, slightly spreading the spring legs 'to decrease springpressure on spheres 34 and 36. Thus, the force needed to move spheres 34and 36 outwardly against spring 26 can be adjusted by screw 48.

External electrical connections to the switch are made through aconventional electrical connector 50 which is electrically connected toa pair of roll pins 52 and 54 embedded in openings in body 16. As isdiscussed below, roll pins 52 and 54 are electrically connected toconductors in contact with spheres 34 and 36 to make up the switchmechanism.

The internal switch structure will become more apparent upon referenceto FIGS. 2 and 3, taken together. The conductive strips 56 and 58 areformed, such as by vapor deposition, from roll pins 52 and 54 down intoconical recesses 33 and 32, respectively. A second pair of strips, 60and 62, are similarly formed on the lower portions of recesses 33 and32, respectively. Strips 60 and 62 are in electrical contact through asmall conductive bead 64 pressed into a small opening between conicalrecesses 32 and 33. The resulting electrical circuit with spheres 34 and36 in place then extends from roll pin 52 through strip 56, sphere 36,strip 60, head 64, strip 62, sphere 34, strip 58 to roll pin 54. Thiscircuit is opened any time inertial forces move either sphere 34 or 36out of the corresponding recesses against the restraining force ofspring 26.

In order that the switch open when a selected inertial impact isreceived, it is important that the switch be firmly mounted with nolooseness slack. Therefore, the switch base is provided with adownwardly extending frusto-conical portion 66 which wedges tightly intocorrespondingly tapered opening 68 in mounting plate 70. The forceholding the switch in place is provided by a pair of straps 72 and 74which engage ears 12. Straps 72 and 74 are in the nature of leaf springsto maintain tightness despite differential thermal expansion of theparts. Bolts 76 and 78 engage strap 72 and bolts 80 and 82 engage strap74 to urge ears 12 downwardly.

The switch embodiment shown in FIG. 1-3 is primarily capable ofresponding to inertial forces from either direction along a single line,that line passing through the centers of spheres 34 and 36. Of course,the switch will respond to forces from other directions approximately inthe direction of this line. An alternative embodiment of the switchwhich will respond to forces from any direction in the plane parallel toplate 70 is shown in FIGS. 4 and 5.

In this embodiment, as seen in FIGS. 4 and taken together, housing issubstantially identical to that shown in FIG. 1-3. Hold-down ears 12 areprovided and tapered lower portion 66 fits into tapered opening 68 tohold the switch in place.

Body 88, however, has four equally spaced cutouts 90, 92, 94 and 96within which four arms of spring 98 fit. Each arm ends with aninsulating pad 100 which, typically, presses a sphere 102 into acorresponding conical recess 104 (FIG. 5) as in the embodimentpreviously described. The spring pressure on the spheres is adjusted bymeans of adjusting screw 48. Again, body 88 is held in place withinhousing 10 by a Belleville spring washer 44.

Conductive strips formed on body 88 electrically connect the roll pins(one of which, pin 54, is shown) to the spheres and the spheres to eachother. A schematic illustration of a typical conductor pattern is shownin FIG. 6. A conductive strip 106 extends downward from roll pin 54 (notshown) and across a portion of recess 104. Another conductive strip 108is formed on recess 104, spaced from strip 106. When sphere 102 is inplace in recess 104 it is in electrical contact with both strips 106 and108. A conductive pin 110 extends through body 88 to connect strip 108to a similar strip 112 on the surface of adjacent recess 114. Whensphere 118 is in place in recess 114, it connects strips 112 and 116. Apin 120 connects strip 116 through body 88 to a similarstrip 122 on theopposite recess 124. Another strip 126 is formed on recess 124, spacedfrom strip 122. When sphere 128 is seated in recess 124, strips 122 and126 are electrically connected. A pin 130 through body 88 electricallyconnects strip 126 to a similar conductive strip 132 on adjacent recess134. Another conductive strip 136 is formed on the surface of recess134, spaced from strip 132. Strip 136 extends upwardly to a second rollpin, not shown. When sphere 138 is seated in recess 134, it electricallyconnects strips 132 and 136. Thus, with all spheres in place,theelectrical path is as follows: from roll pin 54 through strip 106,sphere 102, strip 108, pin 110, strip 112, sphere 118, strip 116, pin120, strip 122, sphere 128, strip 126, pin 130, strip 132, sphere 138,strip 136 and finally to the second roll pin. Movement of any of thefour spheres away from its recess will interrupt this circuit.

Two alternative embodiments of the spring pressure adjusting means areshown in FIGS. 7 and 8. While each is shown used with the four-sphereswitch, each is equally useful with the two-sphere switch embodiment.

FIG. 7 shows a means for independently adjusting each spring arm. Spring140 rests on body 16 within housing 10 as in the previously describedembodiment. Here, however, the center of spring 140 is supported on apin 142. An adjusting screw means 144 is provided in cover 42 above eacharm of spring 140. Downward movement of each screw decreases thepressure applied on the corresponding sphere by the corresponding springarm. Thus, the pressure on all of the spheres may be exactly equalized,or the switch may be-made more or less sensitive to impact from aselected direction by varying the spring pressure on any one sphere.

An embodiment featuring positive switch sealing is shown in FIG. 8.While the previously described embodiments can be sealed by covering theadjustment screw switch with solder, an epoxy resin, etc., only theembodiment of FIG. 8 features both positive sealing and continuedadjustability. As with the previously described switches, a spring 98 issupported on body 16 within housing 10. A cover 148 closes the open endof housing 10. A Belleville spring washer between cover 148 and body 16keeps body 16 in place. In this embodiment, cover 148 has an enlargedcenter portion 150 which bears on spring 98. This center portion 150 isconnected to the edges of cover 148 by a thin web or diaphragm 152. Abar 154 across cover 148 carries a central block 156 in which anadjustment screw 158 is threaded. Upward and downward movement of screw158 moves portion 150 due to the flexible nature of web 152, thusincreasing or decreasing pressure on the central portion of spring 98.

While specific propositions, sizes and arrangements of component partshave been shown in the above illustrations of preferred embodiments,these may be varied, where suitable, within the scope of this invention.For example, any desired number of sphere-andrecess sets may be used, asdesired.

Other variations, ramifications and applications of the presentinventions will occur to those skilled in the art upon reading thisdisclosure. These are intended to be included within the scope of theinvention, as defined in the appended claims.

I claim:

1. An inertia switch comprising:

a. a body having a plurality of recesses formed therein;

b. a plurality of conductive members adapted to removably seat incorresponding recesses;

c. a first and a second fixed conductor secured along the walls of eachrecess so that a member seated in the recess completes a circuit fromthe first conductor through the seated member to the second conductor;

. said fixed conductors and conductive members arranged in series toprovide an electrical circuit through all'of said fixed conductors andmembers seated in recesses which circuit is broken upon movement of anyof said members away from a recess;

e. a spring means comprising a plurality of spring arms extending from acommon base, each arm positioned adjacent to one of said members andbiasing that member toward said corresponding recess; and

f. means to adjust the spring force applied to said members.

2. The switch according to claim 1 wherein said plurality of recessesincludes two conical recesses on opposite sides of said body extendinginwardly toward each other and said conductive members are spherical.

3. The switch according to claim 1 wherein said plurality of recessesincludes four conical recesses arranged in one plane around said body,all of which extend inwardly toward a common point.

4. The switch according to claim 1 wherein said body is mounted within ahousing, said body and housing having corresponding tapered portions,and a biasing means engages said body to force said tapered portionsinto intimate contact.

5. The switch according to claim 4 wherein said housing includes anoutwardly extending frusto-conical portion adapted to be received in acorrespondingly configured opening in a plate to which said housing isto be mounted and mounted means adapted to urge said housing toward saidplate.

6. The switch according to claim I wherein said common base extendsacross one end of said body with said sprin arms extending from saidbase along the sides of said ody and terminating ad acent to eacconductive 8. The switch according to claim 7 wherein a single adjustingscrew presses on the center of said common base, whereby the springforce of all of said spring arms may be adjusted simultaneously.

9. The switch according to claim 7 wherein the center of said common.base is supported by a pin mounted on said body, and an adjusting screwis positioned to bear on said base between said pin and each spring arm,whereby the spring force of each arm may be independently adjusted. 1

10. The switch according to claim 7 wherein said body is mounted withina sealed housing, the end of said housing adjacent to said common basebeing closed by a flexible diaphragm having a center portion bearing onsaid common base, and an adjusting screw external of said housingadapted to force said center portion toward said common base, wherebythe force of said spring arms may be adjusted while maintaining sealintegrity.

1 1. An inertia switch comprising:

a. a housing;

b. a body mounted within said housing;

c. said body and housing having corresponding tapered portions so thatsaid body seats securely in said housing;

d. first spring means urging said tapered portions into contact;

at least one conductive inertial member located in a correspondingrecess in said body;

f. second spring means adjacent to each inertial member biasing saidmember toward said recess;

. electrical current means disposed within and structurally attached tothe surface of said recess adapted to complete an electrical circuitwhen said member is seated in said recess and open said circuit uponmovement of said member from said recess.

12. The switch according to claim 11 further including means to adjustthe pressure applied by each said second spring means to said members.

13. The switch according to claim 11 wherein said housing includes anoutwardly extending frusto-conical portion adapted to be received in acorrespondingly configured opening in a plate to which said housing isto be mounted and mounted means adapted to urge said housing toward saidplate.

14. The switch according to claim 11 wherein said inertial members arespherical and seat in generally conical recesses.

15. The switch according to claim 14 wherein said recesses include fourconical recesses arranged in one plane around said body, all of whichextend inwardly toward a common point.

1. An inertia switch comprising: a. a body having a plurality ofrecesses formed therein; b. a plurality of conductive members adapted toremovably seat in corresponding recesses; c. a first and a second fixedconductor secured along the walls of each recess so that a member seatedin the recess completes a circuit from the first conductor through theseated member to the second conductor; d. said fixed conductors andconductive members arranged in series to provide an electrical circuitthrough all of said fixed conductors and members seated in recesseswhich circuit is broken upon movement of any of sAid members away from arecess; e. a spring means comprising a plurality of spring armsextending from a common base, each arm positioned adjacent to one ofsaid members and biasing that member toward said corresponding recess;and f. means to adjust the spring force applied to said members.
 2. Theswitch according to claim 1 wherein said plurality of recesses includestwo conical recesses on opposite sides of said body extending inwardlytoward each other and said conductive members are spherical.
 3. Theswitch according to claim 1 wherein said plurality of recesses includesfour conical recesses arranged in one plane around said body, all ofwhich extend inwardly toward a common point.
 4. The switch according toclaim 1 wherein said body is mounted within a housing, said body andhousing having corresponding tapered portions, and a biasing meansengages said body to force said tapered portions into intimate contact.5. The switch according to claim 4 wherein said housing includes anoutwardly extending frusto-conical portion adapted to be received in acorrespondingly configured opening in a plate to which said housing isto be mounted and mounted means adapted to urge said housing toward saidplate.
 6. The switch according to claim 1 wherein said common baseextends across one end of said body with said spring arms extending fromsaid base along the sides of said body and terminating adjacent to eachconductive member, and said body is depressed adjacent to the center ofsaid common base, said common base supported on ridges on said bodyadjacent to said depression.
 7. The switch according to claim 6 whereinan adjusting screw means is positioned to press on said common baseadjacent to said depression, whereby the spring force of said springarms may be adjusted by adjusting the pressure on said common base. 8.The switch according to claim 7 wherein a single adjusting screw presseson the center of said common base, whereby the spring force of all ofsaid spring arms may be adjusted simultaneously.
 9. The switch accordingto claim 7 wherein the center of said common base is supported by a pinmounted on said body, and an adjusting screw is positioned to bear onsaid base between said pin and each spring arm, whereby the spring forceof each arm may be independently adjusted.
 10. The switch according toclaim 7 wherein said body is mounted within a sealed housing, the end ofsaid housing adjacent to said common base being closed by a flexiblediaphragm having a center portion bearing on said common base, and anadjusting screw external of said housing adapted to force said centerportion toward said common base, whereby the force of said spring armsmay be adjusted while maintaining seal integrity.
 11. An inertia switchcomprising: a. a housing; b. a body mounted within said housing; c. saidbody and housing having corresponding tapered portions so that said bodyseats securely in said housing; d. first spring means urging saidtapered portions into contact; e. at least one conductive inertialmember located in a corresponding recess in said body; f. second springmeans adjacent to each inertial member biasing said member toward saidrecess; g. electrical current means disposed within and structurallyattached to the surface of said recess adapted to complete an electricalcircuit when said member is seated in said recess and open said circuitupon movement of said member from said recess.
 12. The switch accordingto claim 11 further including means to adjust the pressure applied byeach said second spring means to said members.
 13. The switch accordingto claim 11 wherein said housing includes an outwardly extendingfrusto-conical portion adapted to be received in a correspondinglyconfigured opening in a plate to which said housing is to be mounted andmounted means adapted to urge said housing toward said plate.
 14. Theswitch according to claim 11 wherein said inertial members Are sphericaland seat in generally conical recesses.
 15. The switch according toclaim 14 wherein said recesses include four conical recesses arranged inone plane around said body, all of which extend inwardly toward a commonpoint.